Polymer Rod Seatbelt Retractor with Constriction Seal

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional seatbelt pretensioners using metallic balls or rack and pinion systems face issues with weight, cost, synchronization, low resistance conditions, and maintaining the locked position, leading to potential gas leakage and payback of the seatbelt webbing.

Innovation Solution

A seatbelt pretensioning retractor assembly featuring a polymer rod with a recessed portion and a stopper, which allows for efficient pretensioning without obstructing the rod's movement, while maintaining pressure through a seal member and constriction portion to prevent gas leakage and payback.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If metallic balls or rack and pinion systems are used for pretensioning, then pretensioning function is achieved, but weight and cost increase

Engineering Contradiction:

Improvepretensioning functionVSAvoidweight of driving elements

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent replaces the traditional mechanical driving elements (metallic balls, rack and pinion) with a polymer rod that is pushed by a gas generator. This substitution eliminates the need for heavy metallic components while maintaining the pretensioning function through a simpler, lighter polymer-based mechanism.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the material parameter from metallic to polymer, and replaces multiple discrete driving elements with a single continuous polymer rod. This parameter change significantly reduces weight while maintaining the necessary pretensioning capability through the gas-generated pushing force.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If conventional sealing is used without constriction, then assembly is simple, but gas leakage occurs in low-resistance conditions

Engineering Contradiction:

Improvesealing structure complexityVSAvoidsealing performance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies local quality by adding a constriction portion only at the specific location where the polymer rod exits the tube, rather than complicating the entire sealing structure. This localized modification creates backpressure exactly where needed to prevent gas leakage during low-resistance conditions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of trying to prevent gas leakage through complex sealing mechanisms, the patent inverts the approach by creating a constriction that generates backpressure to push the seal member against the rod, thereby achieving reliable sealing through pressure management rather than mechanical sealing complexity.

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If gas generator pressure is maintained beyond pretensioning stroke, then locked position is maintained, but weight and cost increase

Engineering Contradiction:

Improvelocked position maintenanceVSAvoidgas generator weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent enables the system to maintain the locked position using its own structural features (constriction portion and seal member interaction) rather than requiring continued external pressure from the gas generator. The constriction and seal member work together to self-maintain the locked state after the gas generator completes its initial pushing action.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The gas generator performs its pressure-building action only during the pretensioning stroke, and the structural design (constriction portion) is prepared in advance to maintain the locked position without requiring prolonged gas pressure. This preliminary action approach reduces gas generator weight and operational duration requirements.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The polymer rod design enhances pretensioning performance by reducing weight and cost, improving sealing in low-resistance conditions, and preventing payback without relying on prolonged gas generator pressure.

Implementation Method 1

ignition of the pyrotechnic charge or other combustible material creates gas pressure in a chamber having a piston to impart motion upon a driving element

Methodology Applied

Scientific EffectGas pressure: Pressure Increase

Implementation Method 2

The backpressure is produced by the engagement between the driving elements and the sprocket, so lower backpressure reduces the pressure on a sealing element that trails the driving elements

Methodology Applied

Scientific EffectBackpressure: Pressure Increase

Data Source

PatentEP3782862B1Seatbelt pretensioning retractor assembly including a pretensioner rod

Publication Date: 2023.02.15 AUTOLIV ASP INC

Figure 1
Figure 2
Figure 3

AI summary

A seatbelt pretensioning retractor assembly for use in a passenger vehicle is provided. The pretensioning assembly includes a tube in fluid communication with a gas generator and a driving element disposed therein that travels in a first direction in response to actuation of the gas generator. The driving element includes a polymer rod with a recessed portion. A stopper is coupled to an end portion of the polymer rod. The tube includes a projection extending within the tube adjacent to the exit to define a constriction portion. The constriction portion is sized to permit the recessed portion of the polymer rod to pass therethrough while restricting the stopper from passing therethrough. The polymer rod has a retention feature for releasably engaging the projection.